The invention relates to rubber mixtures which contain microgels and isocyanatosilanes and to vulcanisates produced therefrom. By adding isocyanatosilanes the mechanical properties of the vulcanisates, in particular the elongation properties and the abrasion resistance, are improved without the difference in rebound resilience at 70xc2x0 C. and 23xc2x0 C. being reduced.
Use of crosslinked rubber particles in rubber compounds is described inter alia in the following patent specifications and patent applications: U.S. Ser. No. 5,124,408 (sulphur-modified CR gels), U.S. Ser. No. 5,395,891 (BR gels), DE-A 19 726 729 (SBR gels) and DE patent application 19 701 487.9 (NBR gels). In these publications the complete or partial substitution of carbon black or other inorganic fillers, such as silica, by polymeric fillers based on rubber gels is described. The vulcanisates produced therefrom are particularly suitable for producing rubber articles and tire components, such as tire treads. In particular vulcanisates with rubber gels based on CRxe2x80x94, SBRxe2x80x94, and NBR-microgels exhibit high rebound resilience and therefore a low degree of rolling resistance at 70xc2x0 C. and a low rebound resistance and therefore a high skid resistance in the wet at 23xc2x0 C. The difference in rebound resilience between 70xc2x0 C. and 23xc2x0 C. is characteristic of rubber compounds which contain these microgels. However, the mechanical properties of the microgel-containing vulcanisates are not sufficient for use in industrial rubber articles and in tire components. There are deficits in particular in the level of mechanical vulcanisate properties. There is therefore the need to improve the modulus at 300% elongation and elongation at break and the abrasion resistance.
Production and use of sulphur-containing organosilicon compounds is described inter alia in the following patent publications: DE-A 2 141 159, U.S. Ser. No. 3,873,489, U.S. Ser. No. 5,110,969, U.S. Ser. No. 4,709,065 and U.S. Ser. No. 5,227,425. The positive influence of sulphur-containing organosilicon compounds on the mechanical properties of silica-filled vulcanisates is described in these publications. However, neither the use of sulphur-containing organosilicon compounds in combination with mixtures which contain rubber particles, nor the use of sulphur-free organosilanes in combination with rubber mixtures is taught. The use of isocyanatosilanes to improve the mechanical properties of rubber compounds which contain crosslinked rubber particles is not taught either.
The use of diisocyanates for vulcanisation with natural rubber is also described in O. Bayer, Angewandte Chemie [Applied Chemistry], edition A, year 59, No. 9, p. 257-288, September 1947. The mechanical properties of the vulcanisates obtained are, however, unsatisfactory. Furthermore, the vulcanisates adhere very strongly to the metal parts of the vulcanising moulds. Use of isocyanatosilanes for vulcanisation of rubber compounds which contain rubber gels as fillers is not taught by O. Bayer.
The object was therefore to improve the mechanical value (product of modulus at 300% elongation and elongation at break) and the abrasion resistance (DIN abrasion) of microgel-containing rubber vulcanisates without impairing the difference in rebound resilience at 70xc2x0 C. and 23xc2x0 C.
It has now been found that the above-mentioned aims are achieved by adding isocyanatosilanes to microgel-containing rubber mixtures.
The invention therefore relates to rubber mixtures containing at least one double bond-containing rubber (A), at least one microgel (B) and at least one isocyanatosilane (C), wherein the double bond-containing rubber (A) content is 100 parts by weight, the rubber gel (B) content is 1 to 150 parts by weight, preferably 10 to 20 parts by weight, and the isocyanatosilane (C) content is 0.2 to 20 parts by weight, preferably 1 to 10 parts by weight, and further rubber auxiliary agents and fillers.
Double bond-containing rubber (A) includes rubbers which are designated R-rubbers in accordance with DIN/ISO 1629. These rubbers have a double bond in the main chain. They include for example: